Asteroids jaggy vectors

ieure

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This PCB is working, except for two visual issues:

  • Diagonals are jagged
  • In the very center of the screen, vectors fold over themselves a bit.

Here's a photo: http://i.imgur.com/8qatR.jpg

Suspect the X position counter, but I don't see anything obviously wrong with it on the logic probe. Is this reasonable, or am I on the wrong path?
 
Hi;
I have the exact same issue and thought it was a bad DAC but that was not the case.
Checked the voltages for A/C ripple but that was also not the cause of my woes......
Did you ever find a resolution to your problem, if so, I would greatly appreciate your findings...
Thanks in advance
 
BTW, tried using my HP Logic Comparator on the LS157's but they all come up bad???

The game does play perfect with the exception of the "jagged lines" so I tend to think that those IC's are good, it is just that this cannot be used to test these?

Thanks
 
Thanks for the suggestion but alas I have already done that......

Originally the game did not come up, no display......

Then after some work, got the distorted display......

Then almost perfect with the exception of the squiggly vector......

The cross hatch is wobbly all over, I get a pic of that and post.......

Jeff
 

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Thanks for the suggestion but alas I have already done that......

Originally the game did not come up, no display......

Then after some work, got the distorted display......

Then almost perfect with the exception of the squiggly vector......

The cross hatch is wobbly all over, I get a pic of that and post.......

Jeff

You socketed everything except for that one 4016B analog switch, eh? Curious - how do you know it's OK? :rolleyes:
(EDIT: OK, one of the other TL082 are not socketed either ... damn shadows. LOL)
 
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Uh oh..... I stopped checking the IC's when I got the game to this point.....:eek:

I think I better check that.....

I attached pics in an attempt to show the jagged lines but the pics do not convey the severity of the line jag-nation (?).....

I will check that IC but until then, why do I get all those false positives with the Comparator on the 157's?????

Thanks
Jeff
 

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Uh oh..... I stopped checking the IC's when I got the game to this point.....:eek:

I think I better check that.....

I attached pics in an attempt to show the jagged lines but the pics do not convey the severity of the line jag-nation (?).....

I will check that IC but until then, why do I get all those false positives with the Comparator on the 157's?????

Thanks
Jeff

YMMV - but here is my experience.
1. I don't trust the HP comparator 100% of the time.
2. I don't trust my logic probe 100% of the time.
3. I may trust my oscilloscope >75% of the time.
4. I don't use my logic analyzer, but if I did, to test logic on multiple DIGITAL gates, this likely would be the best choice.

So, that being said, if you had a 4 channel digital scope, you could follow the logic table for the LS157 and see if the outputs follow the input logic.

LS157 datasheet:
http://www.ti.com/lit/ds/snos285a/snos285a.pdf

Also, perhaps the LS157 you are comparing with has different speed than the one soldered to the PCB. So, timing might be off? :confused:

BTW, when I see small disturbances in the vectors across the horizontal lines ... I suspect the counters. Usually the affect is more noticeable than what is shown in your pics. And again, I'll end this with YMMV. :)
 
Thanks for the concise explanation.

So I guess that the Logic Comparator is not the magic wand I thought it would be.....

I'll try the board on another monitor and make sure that is not the issue, thanks for the suggestion.

Jeff
 
Thanks for the concise explanation.

So I guess that the Logic Comparator is not the magic wand I thought it would be.....

I'll try the board on another monitor and make sure that is not the issue, thanks for the suggestion.

Jeff

The golden rules for a comparitor is this;

If it reports GOOD, then it is very likely GOOD.
If it reports BAD, it may be BAD.

In the case of your LS157, you probably noticed that the bank of LEDs lit up were pretty much identical. That's a clue that they may be ok but just not testable by the comparitor.
 
1- Yes, I rebuilt the Powerbrick and A/R power supplies. Also rebuilt the deflection and HV boards...... Including the deflection transistors....
2- Yes, all the outputs were lit on the Comparator on each LS157 I checked, so that would be indicative of the component not being able to be tested in this circuit?

I will be getting more into this tonight and hopefully will have the solution by tomorrow....

Thanks for the help.

Happy Friday

Jeff
 
What did you do to fix the more distorted display you had before? I'm having a similar issue with Tempest at the moment.
 
A couple things on using a comparitor....

They compare chip inputs to chip outputs. If the chip output is on a buss, something else could be changing the bus which is not reflected on the chip input.

Chips that have a state (flip flops for instance), need to be tested from power on, as otherwise the chip under test and your reference chip may be in different states causing a compare failure.

I have an Asteroids with worse vectors than that I have to dig into (I thought it was the DACs, but to have X and Y go out together seems unusual given that the power going into the boards is good, though that is no guarantee they didn't get hit with a surge together).

Good luck with your board, when you find the solution, post it here, others may benefit.

Maybe someone else familiar with debugging the vector machine and output on a roids will post some advice here.
 
What did you do to fix the more distorted display you had before? I'm having a similar issue with Tempest at the moment.

I'm sorry but I do not remember if it was the analog switch or the DAC that cured that ill....... there was too much wrong, I just kept going.....
 
OK, worked on this again tonight.
Dug into the wiring harness as the player controls were working from both sides of the game, for player 1, very strange.
Found that someone hacked the SEC.
The player select was incorrect, the GND was incorrect and the control panel connector were switched as well!
It was so hacked that it actually appeared to be correct!

Anyway, swapped the control panel connectors, properly wired player 1 and player 2 and connected the X-inv correctly as well....

Now I have isolated the problem to the player 2 side, basically.

Overall there is distortion, which can be seen on the crosshatch pattern but the real distortion is on the player 2 side when the display "inverts".

All the alphanumeric characters seem to be punctuated at the intersecting corners with a "dot".

When the player 2 ship blows apart upon impact, the pieces are "wavy" but the player 1 ship does not have the severe of a distortion.

Also, the HS table, when it asks for you initials are a little distorted player 1 but severely distorted player 2.............

In this short video, the first ship is player 1 and the second explosion is player 2:
https://youtu.be/pKGacLFkXW8

Also attached 2 pics of the HS, player 1 then player 2.

Jeff
 

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You socketed everything except for that one 4016B analog switch, eh? Curious - how do you know it's OK? :rolleyes:
(EDIT: OK, one of the other TL082 are not socketed either ... damn shadows. LOL)

BTW, I replaced that last analog switch, I just had to give it a try!

Oh, and I also replaced the 2 X 2n3906's in the Inv-x circuit, they are just too cheap not to have given that a try as well......

Still distorted......
 
Went to the counter section and of course my Logic Comparator was useless on the LS191's......

Piggybacked them onto the LS191's at C9,D9 and E9 and no change for C and E but when on D9, caused more corruption so I pulled and replaced the IC but again - no change.............
 
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